Investigators suspect the vessel, chartered by MSF and the SOS Mediterranee charity and currently stuck in the French port of Marseille, passed off 24 tonnes of potentially toxic waste as ordinary waste, Italian media reported.

MSF bank accounts in Italy have been blocked by the authorities, the international charity said.

Prosecutors in the Sicilian city of Catania are running the inquiry into migrant clothing, food leftovers and sanitary waste that was handled at Italian ports from the Aquarius and the Vos Prudence, another vessel chartered by MSF last year.

We strongly condemn the decision by Italian judicial authorities to request the seizure of the Aquarius for alleged anomalies in its disposal of on-board waste.

The ships have rescued thousands of migrants from the Mediterranean with immigration a hot-button issue in the European Union.

“All our port operations, including waste management, have always followed standard procedures,” MSF said in a statement. “The relevant authorities have not contested these procedures or identified a public health risk since we started our activities at sea.”

“The only crime we see today on the Mediterranean is the total dismantling of the search and rescue system,” said MSF Italy director Gabriele Eminente.

He added in the statement that MSF had suffered “two years of defamatory campaigns” against non-governmental organisations.